Author: P. Epperson

Construction Scheduling. What are the Critical and Near Critical Paths? Why do we care?

When the schedule is developed, the schedule logic should be complete. All activities should have at least one predecessor and one successor, with the exception of the first and last activities for the schedule.

If this is done, the combination of activity durations, activity calendar assignments, and schedule logic create the CPM schedule network. This CPM schedule network is made up of many sequences (logic paths) of activities.

In simple terms, the longest continual path from the project start to the end of the project or the next hard constraint establishes the Critical (Longest) Path.

The Total Float values are a just the product of the forward and backward pass through the CPM schedule network. Just because the Total Float value is zero does not make the activity critical.

However, the Total Float values are important. If the Critical Path has a Total Float value of zero, then the Near Critical Path activities will most likely have a Total Float value very close to zero. I say most likely because the activity calendar assignment has an impact on the Total Float values. But often, this is a simple rule of thumb for determining the Near Critical Path. I like to keep an eye on work that is on the Critical Path first and then also pay attention to work that falls on the Near Critical Path(s) within one or two weeks of the Critical Path for large projects and a few days for small projects.

It’s not unusual for the PM and Superintendent to focus on work on the Critical Path and not pay enough attention to work on the Near Critical Path(s) and then have the Critical Path shift because a lack of progress for the Near Critical Path work took over the Critical Path.

This is just one reason complete logic, calendar definition and assignment, and limiting constraints are important when developing a baseline CPM schedule. If you scatter constraints throughout the schedule, you will not have a true Critical Path for the project. Without complete logic, you do not have the means to accurately complete the forward and backward pass that establishes the CPM schedule network scheduled dates and Total Float values. Without calendar definition and proper assignment to activities, durations will be erroneous and this will ultimately produce a false schedule network.

I know many of you can offer additional comments and recommendations. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Recovering Lost Time or Saving Work for Later?

When the project baseline schedule is developed, most of the relationships used should be Finish-to-Start, FS. There is always the need for Start-to-Start, SS or Finish-to-Finish, FF relationships to model some sequences of work, but it’s best to break the work down enough to schedule with predominately FS relationships.

That said, far too often it seems that progress is not what was planned due to one reason or another. During the update process, assigning the actual dates and expected finishes to current activities pushes the schedule out. Sometimes only a day or so, but sometimes the schedule can push out weeks…..

How do we recover this lost time? How do we plan the remaining work to mitigate the late project finish? How do we keep from turning in a schedule update that the owner will immediately reject with the demand for a “Recovery Schedule”?

Often, there is a mix of activity duration reductions and resequencing of work.

If the parties responsible for the activities agree to the duration reductions and commit to supporting the schedule with additional resources or hours, this is usually not a problem. There may be work area size constraints that limit the effectiveness of more resources, or there may be logistical constraints that limit the amount of work which can be placed. But usually, adding resources or hours, in small quantities can work.

The trouble usually comes from resequencing the work. All too often, the recovery is achieved by taking several activities sequences with FS relationships and making the relationships SS with small lags. Basically, this is modeling the work to have each trade on top of the predecessor work’s trade. Rarely is this successful. What ends up happening is the work gets “stacked”. The work that couldn’t be completed when it was scheduled, with the resources available, is now magically supposed to be completed when other work is demanding more resources and there is less time to complete the work for that area.

Don’t get me wrong, limited resequencing of work is normal and can be done successfully. But it is not the cure-all for lack of progress.

So, how do we efficiently recover the lost time?

In reality, the scheduled finish date is only pushed out by lack of progress for work on the Critical (Longest) Path.  The key is looking at the activities on the Critical Path and finding a way to work with durations and sequencing to shorten this path. This is an iterative process because the Critical Path will shift to the next Near Critical Path as you shorten the current Critical Path.

The thing to remember is not to let work not on the Critical or Near Critical Path sit. Work where you can when you can. But always make sure you’re making adequate progress for work on the Critical and Near Critical Path(s).  If you do this, you won’t have to worry about recovering time!

I know many of you can offer additional comments and recommendations. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Use the Work Breakdown Structure to Verify the Deliverables.

When the project baseline schedule is developed, activities are created that represent work to complete the project. It’s tempting to jump in and start adding activities as you build the project in your mind. Resist this temptation….

First, plan the schedule! How will the schedule be used? How will progress and performance be tracked? Will resource and cost be tracked by cost accounts? What presentation types are required by the contract?

What is going to be the approach to the project execution? Who are the team members? What are the contractual requirements for the schedule? Is there coordination with other work by contractors or the owner required?

Once you’ve answered these, and any other specific questions for the project execution, you should define the deliverable and break the deliverable down into smaller and smaller pieces until you have individual work packages. This helps ensure you get the entire scope of the project in the schedule.

Setting up your resources, cost accounts, activity coding and calendars is also part of the planning phase of developing the schedule.

Now you can start adding the activities to support the deliverables in an organized manner. The best part is this allows the use of mandatory logic for the completion of each work package. This makes it quick and simple.

Next, you can apply the preferential logic to create the phasing you planned earlier in the process. If you organized the WBS by phase, this is easily done as well.

Planning the schedule development and management will help ensure you end up with a complete schedule for the project. It will also make the schedule more useful and easier to manage.

I know many of you can offer additional comments and recommendations. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. What Data Columns Should be Displayed?

Do you ever look at a schedule pdf and wish you had access to more information? Know what the percent complete actually is? What produces the Total Float value?

Would you like to be able to see what is most important to you, as a PM? As an Owner? As a subcontractor?

When your contractor develops the project baseline schedule, they develop a few simple layouts for the project. (Or they should…) We typically set up a Classic Layout with Start, Finish, Percent Complete, Duration….

But we can also set up specific layouts for use by different team members.

However, often what you find in a progress or owner’s meeting is the two or three week look ahead schedule with the Activity ID, Name, % Complete, Duration, and Start & Finish dates. This doesn’t really offer much useful information.

I like to develop several layouts.

One layout that I use has the ID, Name, Physical % Complete, Duration % Complete, Original Duration, Remaining duration, At Completion duration, Start, Finish, and Total Float value. I can use these columns to see variances in duration usage and physical work completion. This quickly alerts me to production issues or potential delays. (It is possible to target previous updates and show actual variance values for duration, start and finish dates).

 

I also like to produce a simple progress update worksheet for the superintendent and field staff to use for keeping track of actual start and finish dates. They can keep these at their desk and mark off the dates as they happen each day. At the end of the month, all they have to do is add the physical % complete for the work still in progress. It’s just that simple. I provide a column for them to enter the date they now expect to finish the in-progress work. Using this expected finish date, we revise the remaining duration and the At Completion duration. This provides us with the Duration % Complete and the At Completion Duration variances which allow us to spot trends and take corrective action quickly.

Those are very simple layouts.

There are options for the Project Team. Let the scheduler show you what they can produce and work with them to find the right layouts with the right data columns that work for you. It will make managing work much easier for everyone.

I know many of you can offer additional comments and recommendations. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Layouts and Options for Layouts.

Do you ever look at a schedule pdf and get lost in the many pages of data and bars?

Would you like to be able to quickly find out what is most important to you, as a PM? As an Owner? As a subcontractor?

When your contractor develops the project baseline schedule, they develop several activity code structures for the project. (Or they should…) We typically set up activity coding for phases, areas of work, subcontractor or trade responsibility, cost accounting source, CSI Division….

We do this so we can assign specific code values to each activity. This allows a filter or sort or group on specific or combinations of activity code values. We can filter by trade and sort by start. We can then group by area or phase or building. There are many ways to view the schedule which can make it easier for everyone.

However, often what you find in a progress or owner’s meeting is the two or three week look ahead schedule. This is a good tool. But, it is a specific tool. The look ahead schedule layout can show the work by phase or area or trade or simply as a “waterfall” by start date. The project team should decide what works best for them and request that layout for each meeting.

There are other layouts, in addition to the look ahead and the entire project schedule that are very useful.

One layout that I always use is the Critical Path (Longest Path) by Start/Finish date with no grouping. This provides a simple view of the critical activities by start date in a “waterfall” view. Very helpful for seeing what is critical and next in line.

 

I also like to produce a filtered list of incomplete and not-started activities sorted by Total Float value and then Start/Finish. No grouping, just a “waterfall” again. This allows us to see what is most likely the Near Critical Path activities by simply going down the list to the paths after the Critical Path. (I use a filter to remove the Longest Path) This is very helpful to the PM and Superintendent. They can ensure they focus on work that is near critical as well as critical. Too often this is missed.

Those are very simple layouts.

There are options for the Project Team. Let the scheduler show you what they can produce and work with them to find layouts that work for your project. It will make managing work much easier for everyone.

I know many of you can offer additional comments and recommendations. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Total Float Values and Calendars.

Do you ever look at a schedule and wonder why a series of related activities will have different Total Float values? Perhaps the activities on the Critical (Longest) Path?

It just makes sense that the activities in the same work path would have the same Total Float value.

However, when your contractor develops the project baseline schedule, they develop the various Activity Calendars for the project. There may be a 7-Day Work Week Calendar for Milestone Activities, Level of Effort Activities, and fabrication or delivery activities. There may be a 5-Day Work Week with Holidays Calendar for work planned for normal work days but not on holidays. There may be a weather calendar with specific days set as non-work days to allow for the anticipated normal weather impact days.

Each calendar will have a different action on the Total Float value because each calendar only allows the work to be scheduled on the work days for that specific calendar. This, in turn, determines the Total Float value.

This is why the Milestone Activities on the Critical Path may have a value of -7 days and the activities on the 5-Day Work Week Calendar may have a value of -5 days.  The 5-Day Work Week Calendar doesn’t take the weekend non-work days into account with the calculation. The total Float value for the activities assigned to a weather calendar would also be different.

This is also why a set period impact to the schedule, such as 30-day delay in receiving direction to start work on a work package could have a larger delay to the contract completion. A 30 Calendar Day impact can push the work over non-work periods such as holidays and weather resulting in a 35 Calendar Day impact to the contract Completion Date. This must be accounted for in the Time Impact Analysis so the party not responsible for the delay is not forced to absorb this variance.

The bottom line is: Don’t let Total Float values determine what is critical, let the schedule software do that by using the Critical Path definition of Critical = Longest Path. Using the Total Float values is valid for many things, but determining your Critical Path isn’t one of them. If you have more than one calendar for the activities, there will be differences in the Total Float values.

I know many of you can offer additional comments and recommendations. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Let Durations Help You.

How can you use the Activity Duration value to help you manage your schedule?

Simple, just look at all the columns and do some math in your head.

When your contractor develops the project baseline schedule, they develop the Original Duration for each activity. How they develop the durations is a subject for another post. But let’s assume they have used historical data, input from subcontractors, calculated productivity and quantities, or some method of developing an accurate value for the each Activity’s Original Duration.

Most Schedule Presentations (Gantt Chart pdf’s) have the activity names, dates, a percent complete and a duration for each activity shown in columns. Then there are the magical bars to the right. Sometimes there are even relationship (logic) lines drawn from activity to activity so you know what drives what, right? Can you actually read it? Doubtful…. Anyway, let’s focus on the duration columns.

If you’re looking at a Schedule Presentation from a Primavera P6 schedule, there are options for which duration columns you can see. Almost everyone uses the Original Duration column. Most of us use the Remaining duration column. That’s all we need to know, correct?

Not really, there is a column that shows the At Completion Duration. This is not seen in presentations that often, probably because we want more room for the magic bars and lines… But this is an important column to be able to see when reviewing a Schedule Presentation pdf.

If you have an Original Duration of 5 days (Work Days or Calendar Days depends on the Calendar. This is a subject for another post), and a Remaining Duration of 3 days and the percent complete (whether it is Physical, Duration, Activity, Performance, or Cost or another type is a subject for another post), is 50%, things are looking good, right?

Not always. If you look at the At Completion Duration, you may find that while the Original Duration is 5 and the Remaining duration is 3. But the At Completion Duration could be 35 or any other value if the activity finish date is riding the Data Date. This can happen depending on the settings used to manage the schedule. Unless you actually look at the dates and do some calculations in your head while reviewing the schedule, when you don’t have the At Completion duration column to use, you may not see the slippage.

Ask your contractor to display the At Completion Duration column for their Progress Meeting Look Ahead Schedules and any other pdf submission. It’s worth the trade off with the magic bars and lines!

Knowing what was planned, what is remaining and what the time impact of activity progress slippage is can save you some trouble.

I know many of you can offer additional comments and recommendations. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Use of Relationship.

When your contractor develops the project baseline schedule, do they use many Start-to-Start (SS) or Finish-to-Finish (FF) relationships? Do you know?

A relationship determines how the successor activity will start or finish relative to the predecessor activity. The most common relationship is the Finish-to-Start (FS) relationship. The scheduled finish date for Activity A determines the scheduled start date for activity B. Unless a lag is assigned, this is simple. (See previous post).

However, often the schedule model requires the use of SS and/or FF relationships. If the activities will actually run concurrent and the activities are broken down to the level of detail necessary to plan and manage the work, this is acceptable. If the relationship includes the assignment of a lag, it may still be acceptable but this relationship should be reviewed and agreed to by all parties.

The problem arises when the series of work activities is developed with SS relationships and there are not any successors to the finish of these activities. These are essentially open ended relationships which means the activity could not finish and still not affect the schedule. This may indicate the work is not developed to enough detail to allow Finish-to-Start (FS) relationships to drive the work. Or the addition of work driven by the activity was missed during schedule development. If this work happens to fall on the Longest Path, this path is now driven only by the start of work for each activity, not by the finish of the work for the activity. In time, these relationships may fall on the Longest Path through updates and out-of-sequence work. personally, I prefer to limit the use of SS relationships in general.

Then there are the Finish-to-Finish (FF) relationships. These force the successor’s scheduled finish date to push out to follow the predecessor’s schedule finish date. This is commonly used to close off SS relationships to model concurrent work with the finish dependency. However, often the only successor is the FF relationship. This creates an open finish, which is much like a missing successor. If the predecessor has only the finish of the concurrent activity to drive, and this relationship is a FF relationship, and the successor has no other predecessor. It effectively has no predecessor to the start of this work. If the predecessor activity has only the successor with a FF relationship, what future work does it drive?

Finally, there is the combination of relationships that create reverse logic. Activity A is a FF to Activity B. Activity C is a SS to activity B. The duration of activity B determines when activity C can be scheduled to start. The start of activity B is not driven by any other work. The finish of activity B is driven by the finish of activity A. If the duration for activity B is increased, unless the start of activity C is driven by another predecessor relationship, the start date for activity C is pulled back to schedule an earlier start. This can have unintended consequences for the schedule. We see this often when the schedule is developed using a lot of SS and FF relationships.

We won’t mention the Start-to-Finish (SF) relationship. This is extremely rare. This says that the start of a predecessor cannot start until the finish of the successor. I have only seen it used intentionally and with an acceptable reason twice. And that was to model work on a rolling wave schedule for which there was not much design detail developed. However, this relationship is sometimes used by mistake.

The SS or FF relationship, if used correctly, can allow the schedule to model the plan. It is my opinion that the use of these relationships should be kept to the absolute minimum and be only used to model actual planned concurrent work which is broken down into the level of detail necessary to plan and control the work.

I know many of you can offer additional comments and recommendations. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Use of Relationship Lags.

When your contractor develops the project baseline schedule, do they use many relationship lags? Do you know?

A relationship lag is an imposed period of time between the predecessor and successor activity. A common use in a Start-to-Start (SS) relationship with a 2-day lag. Perhaps the contractor’s plan is to start finishing drywall 2 days after the drywall installation begins. This allows the work to run concurrently.

There absolutely are times when work can and should be modeled this way. However, care should be taken to ensure an open start isn’t inadvertently created. (This is a future topic)

The problem arises when the series of work activities is developed with SS relationships with an assigned lag. This may indicate the work is not developed to enough detail to allow Finish-to-Start (FS) relationships to drive the work. The issue is, once the start of the predecessor is actualized, the start of the successor is only dependent on the calendar set for use for lags. This may not match the number of days intended. If this work happens to fall on the Longest Path, this path is now driven by a calendar. I prefer to limit the use of SS relationships in general, much less with assigned an assigned lag.

Then there are the Finish-to-Finish (FF) relationships with lags. These allow the successor work to finish only after the predecessor’s finish date plus the lag duration. This is commonly used to close off SS relationships to model concurrent work with the finish dependency. However, often the only successor is the FF relationship with the lag. This creates an issue in itself. (This is a future topic)

The most serious issue is when the relationship is an FS with a lag. What does the lag model? Should there be an activity to establish this difference in the relationship finish to start? Most likely, the answer is yes. There is nothing wrong in using an FS with a lag to have the lag represent say, cure concrete. I personally prefer to add the cure concrete activity with the number of days required. This is more transparent. The lag is not visible and creates a non-work period seen in the Gantt Chart bars and can cause confusion.

Then there is the negative lag, or leads. Many schedulers like negative lags and use them as a viable way to model the plan. When I see an FS relationship with a negative lag, I wonder why the use of a SS relationship with a positive lag could not have been used. The use of the negative lag may better represent the thought that the successor cannot start until 3 days prior to the finish of the predecessor. And this 3 days is the critical period. I personally prefer to model this type of plan with a SS with a lag or to further break down the activities to allow the use of FS relationships to model the work.

Finally, there are the SS relationships with an assigned lag that is larger than the activity duration forcing the model to show the work as an FS relationship. Why not just use the FS relationship? Unless there is a reason to model the work this way, it just doesn’t make sense to do so.

The relationship lag, if used correctly, can allow the schedule to model the plan. It is my opinion that the use of lags should be kept to the absolute minimum and only used to model SS or FF relationships.

But remember, the lag follows the calendar set for use for lag calculation. If the predecessor calendar is set for use, and the predecessor is assigned to a 5-day work week calendar, the lag will follow that calendar and the duration will be in work days. So, a 3-day lag could become a 5-day delay between the relationships if the lag spans a weekend. This may not have been the case when project work was planned and the schedule was developed and the lag did not span a weekend. Remember, this is not transparent, only someone who understands the schedule software and has access to the native file format can verify this. Unless the schedule layout includes the columns which show relationships with lags and the column that shows calendars. Even then, you need to know what the actual non-work days for the specific calendar are.

I know many of you can offer additional comments and recommendations. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Do you Really Need a Scheduler to Develop and Manage the Schedule?

Does an experienced contractor really need a professional scheduler to create the baseline schedule and manage the update and revision process? Not necessarily, many projects can be scheduled using a worksheet or a simple program to model the activities and bars against a timeline.

But, does that typically provide the best schedule for managing the project? Can the contractor benefit from having a schedule professional on their team? Or at least as a third-party consultant?

Budget constraints, lack of staffing, or bad experiences with project scheduling can be some of the reasons a contractor will not have a scheduler on the project team. And, make no mistake, there is cost to this

I can understand why a contractor may be reluctant to use a professional scheduler, to a point. Some projects are simple enough and can be managed this way. Some owner-contractor relationships are strong enough that both parties trust the other will compensate them for delays or late completion.

What about the projects that really should have a schedule professional supporting the contractor with schedule development techniques, best practices and an understanding of what the schedule specifications actually require? What value do they receive when they have that support in place?

First, they should benefit from having the scheduler review the RFP specifications, prior to submitting the proposal, to review and quantify what the schedule specifications require and assist with the budget for schedule development and management. Many contractors see the specification requirement for a “CPM” schedule and assume it means a “P6” schedule or a fully resource and cost loaded schedule. A professional scheduler can interpret the schedule specification and explain the requirements for the development of the baseline schedule and schedule updates. There is much more to it than most people think there is.

Almost all contractors pride themselves on knowing how they can and will build the project, better than their competitors and for less cost than they budget for. I do not doubt this. I’ve met some great Project Managers and Superintendents and they know how to do amazing things when it comes to coordinating work and managing subcontractors.

But, they are great in their area of expertise. They are not necessarily project controls experts or professional schedulers or cost estimators. Those are specific “trades”, just like being a Carpenter or an Electrician. Most of us in the construction industry can do a little of several “trades”, but we cannot be a specialist in many trades. A few can, but I’m not one of them.

That said, a schedule professional can work with the contractor to put their plan in the program, correctly utilizing the program settings and schedule best practices, to model the plan for use by the entire project team. If done correctly, with input from all the trades and the owner, the schedule becomes a map to the completion of the project.

The schedule professional provides this map with the quality and integrity to be accepted by the owner and used to manage the subcontractors, submittals, procurement, deliveries, mobilization, and the coordination of work. The schedule also provides the Project Manager the ability to manage change order impacts to the schedule and measure performance of the various project team players.

Often, owners require the schedule to be updated and maintained as part of the invoice process. The professional scheduler supports this process by applying the actual progress to the schedule and helping the project team with identifying production slippage and schedule impacts as well as modeling revisions as necessary to revise the plan going forward.

A contractor can possibly manage a project without a schedule professional on their team. But, would they manage a project without field superintendence or materials coordination, or subcontractors for specialized work?

It’s tough to quantify what value a professional scheduler brings to the contractor’s team, but there are definitely costs to not having one. A questionable baseline schedule, the inability to project work with confidence, and the inability to accurately quantify change order delays are only a few basic functions that would be lost.

I know many of you can offer additional comments and war stories, for all of us. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP